Actually, a slight revision to the last comment is critical to properly answering the original question: While there IS a federally mandated 'cap' on the amount a student can take out in the form of some federally regulated education-related loans, the upper-limit of only applies to certain types of federally-backed loan programs like the Stafford (both subsidized and unsubsidized) and NOT to others--specifically, not the Graduate Plus loan program.
This can seem a bit strange when the various numbers of federally backed loan programs are in the mix, the differences in the availability and restrictions of loans between undergrad and graduate school, whether one is considered an 'independent' or not--not to mention that there is also a Plus 'Parental' loan program for undergrads who have financial needs beyond the standard Perkins/Stafford program packages and either do not have economic parental contributions to offset the increased needs for financial aid or happen to be undergrads with 'independent' status and no measurably reliable familial financial contributions to fall back on. So the Plus Parental program is utilized at the undergrad level where the parents are responsible for repaying the loan, not the theoretically 'dependent' student. This is different from that of the Plus graduate loan program as grad students are typically labeled 'independents' even if they do have parental funds at their disposal. So for graduate students with rich parents willing to pay for medical school to get Plus graduate loans, they (1) wouldn't qualify based on many loans based on financial need if the parental contributions were made directly to the university's endowment or (2) would have to refuse mom and dad's money 'because I'm an adult!' as if this kind of rebellion helps much of anything or (3) take their parent's money under the table and make sure the university doesn't catch-on to their little 'financial non-need' schemes.
As graduate students are theoretically treated as the responsible party, the obligations of Grad Plus loan repayment fall on their shoulders, rather than parents under the parental program. Yet I admit the characterization of Grad Plus loans as not being 'need-based' is a bit fuzzy... as they are still ideally awarded in order to help students cover the costs of education, living expenses, or the necessities of graduate study. Qualifying them a not 'need-based' is almost as curious as describing them as 'credit based' loans--while it's easier to say, yes, they do have a fixed interest rate and a 'federal guarantee' (ok, um, hope this ends up being a good thing).
The requirements for the Plus Grad loan program are also slightly more stringent than, say, applying for Stafford loans for grad study, but not exactly tricky to navigate or get qualified for. 'Financial Need' remains the key consideration most federal programs focus upon when making decisions regarding whether or not to award federally-backed loans to students, grad or not. There is generally a preference for highlighting the benefits of using other federal alternatives like the Stafford loan programs before applying for extra funding through the Plus Graduate loan honey pot. This is pretty commonsensical advice as the subsudized Staffords accrue no interest while students are in school and the unsubstadized Stafford accrue interest at a lower fixed rate than those of Plus Graduate loan programs.
Not only are the interest rates lower for unsubsidized Stafford loans, they are also easier to get for persons WITH actual financial needs but no/bad credit history than Plus graduate loans because Stafford loans require NO credit checks. The limitations of the Stafford loan programs are, well, that there is a limited amount a student can take out annually, and an aggregate limitation ceiling to how much money a student can take out of Stafford/similar programs over the course of their lifetimes.
The Plus Graduate loan programs do not have these numerical limitations, but are not need-based relative to a student's personal financial situation, and can vary dramatically from one school to the next--due to vast disparities in tuition costs and living expenses. A student going to private schools in expensive urban environments can expect their actual 'financial need' to crush that of someone attending an in-state public institution in a less expensive, more rural area--so the fiscal limitations of Stafford loans may prove more daunting from one student to the next relative to different contexts and costs. For example, as a Virginia state resident my tuition costs at UVA were miniscule relative to any other option in a similar 'best of' university categories. Living expenses were not dire, even if Charlottesville was a relatively more expensive area to live in than other areas of the state outside the beltway. Of course, out-of-state students paid around the same tuition costs as any top private colleges or universities--but at least the living expenses were manageable. Now, choosing to go to Columbia U. for grad school--even in the safer, more gentrified surrounding upper west side--is going to be an investment whether or not you got a so-called 'free ride' like I did. My hefty tuition was covered, but that $12,000 living stipend was a joke. Hello, loan office. It took about a month to realize I was not a huge fan of my chosen Ph.D. program so loaded on the courses, escaped with my MA with little financial scarring, and was wooed to a nicer, friendlier Ivy at UPenn--where the 'free ride's' living stipend went further, although still was laughable.
Professional grad programs like MBA's, law school, med school, or a decent MA in most anything is where grad students can really get gouged by the financial 'corporation' aid industry. Federal loan programs are almost always more flexible with respect to repayment plans and consolidation options, loan forgiveness for certain public sector careers, etc. But private lenders faced far less scrutiny until very recently--and had gotten away with a great deal more at students' expense.
Should you ever get to the point you exceed the 'aggregate maxed-out limits' of the Stafford loan system, grad students are often faced with the choice between two new loan options: the abstract realm of the 'private loan' industry or Graduate Plus loans. In the current economic climate, even though many private loans offer a lower interest rate for those passing a credit check with flying colors--i.e., have great credit or find a co-signer--these lower interest rates are still variable. In today's more wary economic climate, many would rather forgo a lower interest rate which may change, especially if their Fico score and credit report is not super fantastic--like most grad students. Even good credit records don't guarantee low interest rates, especially in the long term. Alternatively, even though Plus Grad loans make students pass an infamous 'CREDIT CHECK' as a requirement along with proving financial need, this is essentially proving that your credit history is not horrendous: no defaults on previous edu loans, no bankruptcy, no unpaid 'past 60-90' day bills from credit cards. Achieving 'BAD CREDIT' sounds pretty hard before you go to grad school and have any decent loans to default on.
The federally mandated cap associated with loans like the Stafford programs do exist--as the other respondent mentioned--and will come into effect if--say, over the course of two MA's and a Ph.D.... or one MBA or an MD--a student hits the upper-echelon of a number in the arena of almost $140, 000. This cap does not include, however, Grad Plus loans--in other words, if you run up an respectable $140, 000 tab just in public, federal funding without ever being forced to bite the more precarious private loan bullet, Grad Plus loans can still be applied for and approved as they are not included in this governmentally mandated federal loan cap.
This said, you can't go nuts with them--while 'financial need' may not be a main consideration and the 'credit check' rather difficult to fail, the school still gets to determine how much of a GradPlus loan is distributed as the educational budget of the school is more or less the defining rationale shaping whether or not a student will be approved for a Graduate Plus loan of any financial significance. So even though there is no cumulative cap on how much a given student can borrow under the Grad Plus loan program, the amount a student qualifies for is related to the financial need the school understands as a part of an overall student's budget, and then also after any other known financial aid/scholarships are taken into account.
Thus while there is an upper limit to how much a student can take out in the form of Stafford loans both annually and over the overall life of the student's schooling, the aggregate limit which applied to loans subsidized by the gov't and those like the Stafford (sub/unsub) does NOT include a credit check and has a more attractive interest rate. And while actual 'financial need' is not taken into account in terms of one's personal bank account or recorded economic mobility, the Grad Plus loan is not exactly 'free money' despite a required-but-difficult-to-mess-up credit check. While there is no official annual or lifetime aggregate limits, the interest rate is higher than loans like the Stafford programs--and the Grad Plus loan distribution amounts are determined according to school protocols:
"Loan eligibility not based on need
Loan eligibility and total loan amount is not based on household family income level, personal income level, financial need, or personal assets. GradPLUS loan borrowers will have to pass a credit-check.
How much can I borrow with a GradPLUS loan?
The yearly limit on a Graduate PLUS Loan is equal to your cost of attendance* minus any other financial aid you receive. For example, if your cost of attendance* is $60,000 and you receive $40,000 in other financial aid, you could borrow up to but no more than $20,000." (this is your generic summary found on the web)
So there are no 'definitive numerical limits'--but limitations all the same.
The problem with many graduate programs, of course, that the upper-limits of applying for the more 'preferred' Stafford loans one year at a time is less and less likely to be enough to cover the costs of many graduate degree programs--and that's just the tuition, not the inclusion of finding money or loans to cover basic living costs. So while you should try to use these non-Plus, 'Direct' Stafford/Perkins loans first (especially if financial need is, well, an undelightful pandemic of graduate school students the world over--and an easy way to qualify yourself for these loans), if you find yourself running fiscally short (like WAY short depending on your grad program of choice), you will likely have to deliberate upon other options including the Grad Plus loan system or (gasp!) various others funding programs run by private foundations like the questionable Mrs. Sallie Mae program.
Also keep in mind that a potentially useful upside to the Grad Plus program over most private lending agencies is that Grad Plus loans can (1) be consolidated with other federal financial aid received and (2) also have comparably better loan repayment options like other federal loan programs--a big plus over the more unpredictable private lending industry, at least for the time being.
good luck,
J
